‘Tooth’ Be Told, We’re Fascinated by Sharks

By Mark Tosh

Thursday, July 26, 2018 3:00 PMIt’s probably safe to assume that everyone has an opinion about sharks. They’re just not the kind of thing you can be ambivalent about.

And sharks were on our mind this week, thanks to the Discovery Channel’s celebration of “Shark Week,” a week-long TV programming block created by the Discovery Channel. This actually is the 30th anniversary of “Shark Week,” which means there’s a whole segment of the population who have been around less time than this cultural phenomenon.

Sharks, believe it or not, are somewhat misunderstood (aren’t we all, to a degree?) and they have under-appreciated eyesight characteristics. More on this in a moment.

Shark Week began Sunday, July 22, and continues through Sunday, July 29. According to NPR, Discovery this year is airing such specials as Alien Sharks: Greatest Hits, Cuba's Secret Shark Lair, Shark Tank Meets Shark Week, and Sharks Gone Wild, among others. “Shark Week is now fully exploiting every other cliche in reality/unscripted television: celebrities, food shows, baby animals, nudity, brand extensions ... this thing is a machine,” NPR noted in its report on the “The Whole Tooth About the Real Meaning of Shark Week.” (Apologies to NPR for co-opting this headline.)

Shark Week originally aired July 17, 1988, and has earned a place as the longest-running cable television event in history, according to The Atlantic magazine. Shark Week, which was originally set out to focus on conservation efforts and correcting some of the misconceptions about sharks, has enjoyed a surge in popularity over the past few years. The content of Shark Week also has evolved to become more entertainment oriented with a focus on fictional documentaries.

Note that Shark Week is broadcast in more than 72 countries and is promoted by the Discovery Channel and millions of its fans via social media. @SharkWeek has its own verified Twitter account, with 283,000 followers.

So in honor of this year’s Shark Week, here are five facts about a shark’s eyesight that you may not have known (according to SharkSavers.org) and five just generally “fun” facts about sharks from DoSomething.org, a global movement for “doing good.”

Sharks are so sensory adept they can detect the slightest amounts of electric current or vibrations (electroreception) and chemical changes in the water (chemoreception). Initially, some believed this acute perception was a way for sharks to compensate for poor vision, but this is no longer seen as true.

About 50 years ago, researchers discovered that shark eyes have duplex retinas, or retinas containing both rod and cone cells. Rods enable the shark to see light and darkness, while cones allow for the detection of color (though scientists are still unsure how sharks interpret colors).

The eye structure of a shark is similar to other vertebrates in that it contains a cornea, lens, retina, pupil and iris. Given their similar structure and usage, shark eyesight works similarly to that of humans.

Shark eyes have a tapetum lucidum, or a layer of mirrored crystals that sits behind the retina (human eyes don’t have this crystal layer). This crystal layer provides a means for light that initially escaped detection to be detected as it is passed through the retina a second time. This, in part, enables sharks to see even in dark or murky water and up to 10 times greater than humans in clear water.

Also unlike humans, shark eyelids serve to protect the eye when attacking prey. Some sharks have a nictating membrane, or a clear membrane that covers and protects the eye when a shark bites its prey.

You are more likely to be bitten by another person than by a shark.

Sharks are killed by the millions annually to supply demand for their fins, which are made into soup and eaten as a status symbol.

The film “Jaws”—though heavily fictionalized—was based on a real incident in 1916, where four people were killed by a shark off the coast of New Jersey.

The eyes of hammerhead sharks are on the sides of their heads, so they have almost a 360-degree line of sight. This panoramic view is inhibited by two blind spots, one in front of the snout and the other directly behind the head.